The War Powers Resolution (aka "Act") of 1973 was created to prevent presidents from doing exactly what President Obama wants to do in Syria. It is the law of the land. What makes him think he has the right to flout it?
In his draft legislation to Congress Obama says what he is proposing is "consistent" with sections 8(a)(1) and 5(b) of the War Powers Resolution (full text at http://avalon.law.yale.edu/20th_century/warpower.asp), which require that he obtain "specific statutory authorization" from Congress absent "a declaration of war" or "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces."
So everything hinges on convincing Congress that what he says in his draft legislation is true -- that an attack on Syria will
(1) prevent or deter the use or proliferation (including the transfer to terrorist groups or other state or non-state actors), within, to or from Syria, of any weapons of mass destruction, including chemical or biological weapons or components of or materials used in such weapons; or
(2) protect the United States and its allies and partners against the threat posed by such weapons.
The first point, then, is that Obama does NOT have the right to attack Syria unless Congress approves. And this is hardly a minor point. Why does the president and his supporters have such a perverted understanding of the law of the land, and why do we as a people even consider allowing him to get away with it? The fact that other presidents have violated this law and that "all presidents since 1973 have declared their belief that the act is unconstitutional" (according to the Wikipedia article) is hardly an excuse, unless "we the people" (like our presidents) have truly given up the idea of the rule of law.
The second point is whether what Obama says about Syria is true. Here there is much room for debate. It has certainly not been convincingly demonstrated that Syria used chemical weapons, and there is apparently also evidence that the "rebel" groups supported by the US have used them. Whether or not and how the proposed attacks would prevent or deter their use or protect the United States is also extremely unclear.